In semiconductor processing, there is a need to obtain precise temperature measurement of a semiconductor wafer during certain fabrication process steps. Accurate temperature measurement is an important part of fabrication process control. Since temperature measurement of the front side of the wafer is often more desirable as the front side temperature determines the process characteristics, the temperature measurement has to be performed without contacting the wafer surfaces. Contacts made to the wafer front side will contaminate the wafer and damage the fabricated devices. Furthermore, contacts made to the wafer surface cause undesirable perturbation of the local wafer temperature. Therefore, a non-contact approach to wafer temperature measurement is desired.
Radiation pyrometry is a non-contact temperature measurement technique which measures radiation emitted by a hot body at certain limited band of wavelengths. This technique is generally accurate, fast, and easily implemented. However, as fabrication process development moves toward low temperature processing, temperature measurement using pyrometry becomes unsuitable. One disadvantage of the pyrometry technique is that temperature measurement becomes increasingly noisy at lower temperatures (below 600.degree. C.). Where a typical cold-wall chemical vapor deposition process operates in the temperature range of 450.degree. C. to 850.degree. C., accuracy of temperature measurement below 600.degree. C. is imperative. Another disadvantage of pyrometry is that it is sensitive to spurious radiation and cannot differentiate between radiation emitted from the wafer and radiation reflected from or transmitted through the wafer. In wafer fabrication where the wafer is often heated on the backside, radiation transmitted through the wafer from the heat source can obscure pyrometry temperature measurement substantially. Thus, pyrometry is not a feasible temperature measurement technique during a number of wafer processing steps.
Besides semiconductor processing, other manufacturing processes also frequently require precise in situ temperature measurement of a body in a non-contact mode. Consequently, there is a need for a non-contact temperature measurement method and apparatus capable of providing accurate temperature measurement over a temperature range of at least 0.degree. to 1,000.degree. C.